The present invention relates to a linear driving mechanism which is arranged in electronic component mounting apparatus such as electronic component loading apparatus and linearly drives an object to be driven such as loading head.
In the electronic component mounting apparatus such as electronic component loading apparatus, the linear driving mechanism is generally used for a head transfer mechanism for transferring a working head such as loading head. Recently, a type of a linear driving mechanism using a linear motor for a linear motion is increasingly used for the linear driving mechanism, instead of a conventionally used linear driving mechanism of a ball-screw type in which a rotational motion by a motor is converted to the linear motion using a ball screw (for example, see JP-A-2002-299892.).
In the linear mechanism, thrust given by the linear motor is exerted on ends of a transfer beam equipped with the loading head. In the above example, the linear motors are disposed close and parallel to guide rails similarly as an arranged position of the ball screw in the conventional apparatus of the ball-screw drive type.
The linear driving mechanism using the linear motor are characterized by high-speed operation and high position accuracy, and the transfer beam driven by the linear motor performs highly accelerated start-and-stop actions at high frequency. Therefore, there have been the following problems in the linear driving mechanism having the configuration due to the fact that the arranged position of the linear motor is located near the guide rail.
When the transfer beam is driven by the linear motor, the position of the center of gravity of the transfer beam is an active position of inertial resistance in acceleration and deceleration. However, in the above-mentioned configuration, a position of thrust generated by the linear motor is significantly distant from a center of the inertial resistance of the transfer beam, and twisting moment is exerted on the transfer beam due to the inertial force in acceleration and deceleration. Therefore, the transfer beam is deformed due to the twist, which affects on accuracy of loading by the loading head, and the twisting moment is applied to a guide mechanism at high frequency, causing life shortening of guide mechanism components.